I can predict that the Eagles merchandise is going to be selling above average until about April of 2019.
After looking at multiples teams, I was able to concude that merchandise is sold at an above average rate for roughly 19 months because of a win in the Super Bowl.
There is also a relationship between how recent the championship was and the nation-wide range of fans searching for merchandise.
The Eagles, the team that won the Super Bowl most recently, had the largest geographical range for searchs. The Seahawks, the second most recent team to win out of the teams I used, had the second largest geographichal range.
The Packers who won the longest time ago, had the most confined range for searchs.